Cooking vessels (saucepans, frying-pans, etc.) are normally fitted with handles to enable the vessels to be gripped easily, even when hot; for which purpose, the best handles are obviously those with good thermal insulation properties.
Some known handles are made from thermosetting polymer materials, e.g. filled phenol-formaldehyde resins: though good thermal insulators, such materials have poor mechanical characteristics, are not easy to work into complex shapes, cannot be coloured as required, and are therefore poorly suited to the manufacture of handles with predetermined functional or aesthetic characteristics (e.g. mechanical strength, form and colour). Moreover, as is well known, such materials have a tendency to deteriorate in appearance, especially as a result of frequent washing.
Other handles are known in which a part made of phenol-formaldehyde resin (or other similar thermosetting material) is covered with or fitted to a part made of thermoplastic material, the well-known, favourable properties of which may thus be exploited to achieve any shape or colour of the thermoplastic part. This, however, poses the further problem of ensuring firm connection of parts made of different, normally incompatible materials. Handles, for example, are known in which a sheath of thermoplastic material is fitted over and secured to a core of thermosetting material using appropriate fastening means (screws or rivets). The thermoplastic sheath is also known--e.g. European Patent Application EP-A-808600--to be co-molded directly onto the thermosetting-resin part.
Besides requiring specially designed additional components (the fastening elements), mechanically connecting the two (phenol-formaldehyde-resin and thermoplastic) parts obviously also involves a fairly long assembly process, both of which result in an increase in overall production cost. Moreover, should the user wish to separate the parts made of different materials, e.g. to wash them differently, this involves yet another relatively painstaking operation, providing, of course, reversible fastening means (e.g. screws) have been used. On the other hand, co-molding two materials of substantially different physical and chemical characteristics calls for accurate control of the molding process, is a complex, relatively high-cost operation, is poorly suited to the formation of highly complex shapes, and obviously precludes any possibility of separating the two parts made of different materials.